Verified answer

3 sec(x)^2 - 4 = 0

3 sec^2 x = 4

sec^2 x = 4/3

sec x = +/- 2/√3

cos x = +/- √3/2

cos x = cos ( 2n pi +/- pi/6 )

x = 2n pi +/- pi/6 where n = 0,1,2,3,4,5,6........

3*sec²(x) - 4 = 0

sec(x) = +/- 2/√3

cos(x) = +/- √3/2

x = pi/6, 5pi/6, 7pi/6, 11pi/6

on the interval [0, 2pi].